An asynchronous successive approximation register analog-to-digital conversion (ASAR ADC) circuit is a common analog-to-digital (A/D) converter. FIG. 1 illustrates a conventional ASAR ADC 10, which often includes a comparator (Comp) circuit 102, an XOR gate circuit 103, an asynchronous successive approximation register (ASAR) logic circuit 104, and a digital-to-analog conversion (DAC) circuit 101.
In the conventional ASAR DAC circuit 10, the input signal Vin is connected to the comparator circuit 102. The comparator circuit 102 outputs voltages Vcomp at the output terminals. The output terminals of the comparator circuit 102 are connected to the XOR gate circuit 103 and are further connected to the ASAR logic circuit 104. The ASAR logic circuit 104 performs a logical operation based on the input signal Vin and generates a digital signal Vout as an output signal. The outputted digital signal Vout is connected to the control signal input terminal of the DAC circuit 101. The output signal of the DAC circuit 101 is connected to the other input terminal of the comparator circuit 102.
Compared to a synchronous successive approximation register analog-to-digital conversion (SSAR ADC) circuit, an ASAR ADC circuit is faster. However, the comparator circuit in a conventional ASAR ADC circuit often has metastable state behavior or other metastable state issues.